1. Field of the Invention
The present invention relates to an electric motor having a rotor and a manufacturing method therefor, and more specifically, to an electric motor capable of simple balance adjustment and a manufacturing method therefor.
2. Description of the Related Art
A rotor of an electric motor requires high-accuracy balance. If the mass distribution of a member that constitutes the rotor is deflected so that the center of gravity is deviated from the axis of rotation, for example, the rotor shakes as it rotates and applies an undesired load to the rotating shaft member.
The following methods for avoiding such an awkward situation occurring are known; (a) loading the rotor with resin, (b) cutting the rotor, and (c) fitting a washer on a projection that protrudes outward from the rotor.
However, these conventional methods involve the following problems. First, the method (a) in which the balance is adjusted by loading resin into the rotor requires a process of curing the resin as well as equipment for loading the resin, so that it lacks in simplicity and economical efficiency. Further, the manufacturing cycle time lengthens by a margin corresponding to the resin curing time, thereby influencing the productivity. If the resin is not cured satisfactorily, it may possibly leak out of the rotor.
According to the method (b) in which the balance is adjusted by cutting the rotor, cuttings may possibly be produced and adhere to the rotor. In some cases, moreover, the cutting work may damage the rotor entirely or partially.
According to the method (c) in which the balance is adjusted by fitting an elastic member on a projection on the rotor, furthermore, the volume of the space that is occupied by the rotor during rotation increases, so that the capacity of the electric motor must be increased correspondingly. Thus, miniaturization of the motor is hindered.